1. Field of the Invention
The present invention relates to a novel method and apparatus for providing ring electrodes of the type that are typically found at the distal portion of a body implantable lead or electrode, the function of such ring being either to provide electrical stimulation to a portion of the body or to sense spontaneous electrical signals associated with muscular movement within the body. More specifically, the invention further provides a method and a construction for a novel multielectrode stimulating or sensing lead, for example, a lead of the type that finds utility in neural stimulators.
2. Description of the Prior Art
It has long been understood that it is desirable for body implantable leads possessing ring electrodes performing a sensing or stimulating function to have an isodiametric configuration. That is, a preferred lead configuration would typically include an insulated and flexible conductor having a circular cross section that is fitted with one or more ring electrodes in such a fashion that the outer surface of the ring electrode is isodiametric with respect to the remainder of the lead. The isodiametric configuration minimizes the difficulty in passing the lead through a vein or through tissue. The smooth surface also minimizes the formation of potentially harmful thrombi when the lead is implanted. Such isodiametric construction has been achieved in different ways.
For example, Beranek, U.S. Pat. No. 4,592,372, discloses achieving an isodiametric configuration of an electrode assembly in a cardiac pacing lead by compressing a metallic sleeve which constitutes the ring electrode just far enough so that its outer diameter is the same as the outer diameter of the flexible body of the lead itself.
In Blake, et al., U.S. Pat. No. 3,995,623, there is proposed a construction for a lead useful in cardiac monitoring and temporary transvenous pacing which has multiple ring electrodes. Those ring electrodes are constructed from a coil strip of spring metal which appears to be crimped upon the electrode body with overlapping ends of the strip being joined to secure the ring electrode.
In Beranek, U.S. Pat. No. 4,608,986, a multiple lumen pacing lead having multiple ring electrodes is disclosed. Although there appears to be minimal disclosure concerning the actual method of construction of the ring electrode, it would appear from the drawings that one of the crimping techniques discussed in the above patents is used to accomplish the construction.
In Peers-Trevarton, U.S. Pat. Nos. 4,437,474 and 4,458,695 a multipolar pacing lead construction having multiple ring electrodes in an isodiametric arrangement is again disclosed. In that construction, the ring electrodes appear to be received in annular slots formed between a series of insulators which are passed over the coiled conductor of the lead and presumably cemented in place with the spaces between these insulating elements defining the slots or annular spaces for the ring electrodes.
Likewise it has been known in the prior art to build an isodiametric lead with spaced ring electrodes by cementing of gluing short sections of precut tubing onto a lead body using the appropriate adhesives and using cylindrically shaped ring electrodes that are isodiametric with the tubing as the ring electrodes. Medtronic, Inc., the assignee of this application, has offered for sale a lead for spinal cord stimulation, the Model 3487A lead, fabricated in such a manner. Conductors from within the lead body can be led through to the underside of the ring electrodes and attached to the electrodes with a laser weld. Such a construction method is labor intensive and costly.
The Model 3487A lead utilizes a coiled conductor set to traverse the lead and provide the electrical path between the ring electrodes at the distal end of the lead and the connector block which connects the lead to the stimulator device. Such coiled conductors have long been used for such applications. However, improvements in non-coiled types of conductor wire afford various benefits including improved resistance to flex fatigue, improved flexibility, and better crush resistance.
It has also been understood in the art that ring electrodes and isodiametric leads can be constructed with a multiple lumen interior with conductors from the various lumens being passed through the insulation covering the lead body to make contract with the underside of electrodes along the lead body, typically ring electrodes.